Although most animals can make vitamin C from scratch, humans have lost the ability over the course of evolution. We must get it from food, chiefly fresh fruits and vegetables. One of this vitamin's main functions is helping the body manufacture collagen, a key protein in our connective tissues, cartilage, and tendons.

From ancient times through the early nineteenth century, sailors and others deprived of fresh fruits and vegetables developed a disease called
scurvy. Scurvy involves so-called scorbutic symptoms, which include nonhealing wounds, bleeding gums, bruising, and overall weakness. Now we know that scurvy is nothing more than vitamin C deficiency.

Scurvy was successfully treated with citrus fruit during the mid-1700s. In 1928, when Albert Szent-Gyorgyi isolated the active ingredient, he called it the anti-scorbutic principle, or ascorbic acid. This, of course, is vitamin C.

Vitamin C is a powerful
antioxidant
that neutralizes damaging natural substances called free radicals. It works in water, both inside and outside of cells. Vitamin C complements another antioxidant vitamin,
vitamin E, which works in lipid (fatty) parts of the body.

Vitamin C is the single most popular vitamin supplement in the United States and perhaps the most controversial, as well. In the 1960s, two-time Nobel Prize winner Dr. Linus Pauling claimed that vitamin C could effectively treat both cancer and the common cold. Subsequent research has mostly discounted these claims, but hasn't dampened enthusiasm for this essential nutrient. The vitamin C movement has led to hundreds of clinical studies testing the vitamin on dozens of illnesses; at present, however, no dramatic benefits have been discerned.

Requirements/Sources

Requirements

Vitamin C is an essential nutrient that must be obtained from food or supplements; the body cannot manufacture it. The official US and Canadian recommendations for daily intake are as follows:

Infants

0-6 months: 40 mg

7-12 months: 50 mg

Children

1-3 years: 15 mg

4-8 years: 25 mg

9-13 years: 45 mg

Males

14-18 years: 75 mg

19 years and older: 90 mg

Females

14-18 years: 65 mg

19 years and older: 75 mg

Pregnant Women

18 years old or younger: 80 mg

19 years and older: 85 mg

Nursing Women

18 years old or younger: 115 mg

19 years and older: 120 mg

Note:
Smoking cigarettes significantly reduces levels of vitamin C in the body.1
The recommended daily intake for smokers is 35 mg higher across all age groups.

Vitamin C supplements are available in two forms: ascorbic acid and ascorbate. The latter is less intensely sour.

Sources

Most of us think of orange juice as the quintessential source of vitamin C, but many vegetables contain as much or even more. The National Institutes of Health's Office of Dietary Supplements offers this list of foods that are high in vitamin C:188

Food

Serving size

Vitamin C content
(milligrams [mg])

% Daily Value

Sweet red pepper, raw

½ cup

95

158

Orange juice

¾ cup

93

155

Orange

1 medium

70

117

Grapefruit juice

¾ cup

70

117

Kiwifruit

1 medium

64

107

Green pepper, raw

½ cup

60

100

Broccoli, cooked

½ cup

51

85

Strawberries, fresh

½ cup

49

82

Brussels sprouts, cooked

½ cup

48

80

Grapefruit

½ medium

39

65

Broccoli, raw

½ cup

39

65

Tomato juice

¾ cup

33

55

Cantaloupe

½ cup

29

48

Cabbage, cooked

½ cup

28

47

Cauliflower, raw

½ cup

26

43

Potato, baked

1 medium

17

28

Tomato, raw

1 medium

17

28

Spinach, cooked

½ cup

9

15

Green beans, cooked

½ cup

8

13

One great advantage of getting vitamin C from foods rather than from supplements is that you will get many other potentially healthful nutrients at the same time, such as bioflavonoids and carotenes. However, vitamin C in food is partially destroyed by cooking and exposure to air, so for maximum nutritional benefit you might want to try freshly made salads rather than dishes that require a lot of cooking.

Vitamin C Deficiency

Scurvy, the classic vitamin C deficiency disease, is now a rarity in the developed world, although a more subtle deficiency of vitamin C is fairly common.2-6 According to one study, 40% of Americans do not get enough vitamin C.7 In fact, vitamin C deficiency sufficient to cause bleeding problems during surgery turns out to be more common than previously thought.141

Aspirin and other anti-inflammatory drugs might lower body levels of vitamin C,8-10
as might
oral contraceptives.11-15
Supplementation may be helpful if you are taking any of these medications.

Therapeutic Dosages

Ever since Linus Pauling, proponents have recommended taking vitamin C in enormous doses, as high as 20,000 mg to 30,000 mg daily. However, some evidence suggests that there might not be any reason to take more than 200 mg of vitamin C daily (10 to 100 times less than the amount recommended by vitamin C proponents).16
The reason is that if you consume more than 200 mg daily (researchers have tested up to 2,500 mg) your kidneys begin to excrete the excess at a steadily increasing rate, matching the increased dose. Your digestive tract also stops absorbing it well. The net effect is that no matter how much you take, your blood levels of vitamin C don't increase very much.

However, there are some flaws in this research. It is possible that vitamin C levels might rise in other tissues even if they remain constant in the blood. Furthermore, this study did not evaluate the possible effects of taking vitamin C several times daily rather than once daily.

Many nutritional experts recommend a total of 500 mg of vitamin C daily. This dose is almost undoubtedly safe. Others recommend that you take as much vitamin C as you can, up to 30,000 mg daily, cutting back only when you start to develop stomach cramps and diarrhea. This recommendation seems based more on a semi-religious enthusiasm for the vitamin C than on any evidence that such huge doses of the vitamin are good for you.

Intravenous vitamin C can easily raise vitamin C levels to a level 140 times higher than the maximum achievable with oral vitamin C.152
However, there is no meaningful evidence that intravenous vitamin C provides any medical benefits.

Regular use of vitamin C does not seem to help
prevent colds.86,146,185 One exception is the “post-marathon sniffle”—colds that develop after heavy exercise.19,20 Vitamin C may be helpful for preventing this condition, although not all studies agree.153

A review of 3 randomized studies involving 2,335 people found that vitamin C may reduce the risk of pneumonia in adolescents and adults, .187
The benefits of vitamin C appeared to be largely restricted to people at an increased risk of getting pneumonia and those with low dietary intake of the vitamin. The authors concluded that the widespread use of supplemental vitamin C to prevent pneumonia was not supported by their review.

Two double-blind studies suggest that the use of vitamin C combined with
vitamin E
might slightly reduce the risk of developing
preeclampsia, a complication of pregnancy.21,169 However, a much larger follow-up study failed to find benefits.170

Two studies conducted by a single research group have found that vitamin C at a dose of 500 mg daily might help prevent reflex sympathetic dystrophy, a poorly understood condition that can follow injuries such as fractures.110,180

Over time, the body develops tolerance to drugs in the nitrate family (such as
nitroglycerin). Some evidence suggests that use of vitamin C can help maintain the effectiveness of these medications.142-145

Other small double-blind trials suggest that vitamin C might be helpful for
anterior uveitis
(when taken in combination with
vitamin E),52autism,40easy bruising,29minor injuries,41 protecting the liver in nonalcoholic steatohepatitis,154 speeding recovery from bedsores,37
treating
female infertility (specifically, a condition called "luteal phase defect"),155
and preventing early rupture of the chorioamniotic membranes ("the water breaking") in
pregnancy.156
Vitamin C might also improve the effectiveness of antibiotic treatment for
Helicobacter pylori, the cause of most
peptic ulcers.179
Given the limited nature of this research, however, further studies are needed to conclude that vitamin C is beneficial for these conditions.

Preliminary evidence suggests that cream containing vitamin C may improve the appearance of
aging or sun-damaged skin.50,51,157
Inconsistent evidence suggests that oral or topical vitamin C, taken by itself or in combination with
vitamin E, may also help
protect the skin against sun damage.42-49

Intravaginal use of vitamin C tablets might be helpful for non-specific vaginitis.159

Observational
studies indicate that people with a higher intake of vitamin C have a lower incidence of
macular degeneration,
heart disease,
cancer, and
osteoarthritis.22-27,59-66
However, these findings do not indicate that vitamin C
supplements
will help prevent or treat these conditions.
Observational studies are notoriously unreliable for showing the efficacy of treatments; only double-blind studies can do that. (For more information on why double-blind studies are so important, see
Why Does This Database Rely on Double-blind Studies?
) Two large double-blind trials exploring the effectiveness of vitamin C for heart disease prevention—one in women at high risk
181
and the other in men at low risk—
183
failed to find any benefit at all.

Vitamin C has been proposed as a
treatment for cancer, but this claim is very controversial, and there is as yet no scientifically meaningful evidence that it works.67-70

Massive doses of vitamin C have at times been popular among people with
HIV infection based on highly preliminary evidence.71,72 An observational study linked high doses of vitamin C with slower progression to AIDS.73 However, a double-blind study of 49 people with HIV who took combined vitamins C and E or placebo for 3 months did not show any significant effects on the amount of HIV detected or the number of opportunistic infections.74 Furthermore, one study found that vitamin C at a dose of 1 g daily substantially reduced blood levels of the drug indinavir, a protease inhibitor used for the treatment of HIV infection.160
This could potentially cause the drug to fail.

A large, 8-year trial involving 11,545 physicians aged 50 years and older concluded that vitamins C and E, alone or in combination, did not lower the risk of
cataracts.186

According to a double-blind, placebo-controlled study of 141 women with
cervical dysplasia
(early cervical cancer), vitamin C, taken at a dosage of 500 mg daily, does
not help to reverse the dysplasia.75

What Is the Scientific Evidence for Vitamin C?

Colds

As the most famous of all natural treatments for the
common cold, vitamin C has been subjected to irresponsible hype from both proponents and opponents. Enthusiasts claim that if you take vitamin C daily, you will never get sick, while critics of the treatment insist that vitamin C has no benefit at all.

However, a cool-headed evaluation of the research indicates something in between. Numerous studies have found that vitamin C supplements taken at a dose of 1,000 mg daily or more throughout the cold season
can
modestly reduce symptoms of colds and help you get over a cold faster, but they do
not generally help prevent colds.81,83,146,162,185

Reducing Cold Symptoms

Most studies on vitamin C have evaluated the potential benefits to be gained by taking vitamin C throughout the cold season. A review of 29 placebo-controlled trials involving over 11,000 people found that the use of vitamin C in this way can reduce symptoms and decrease the duration of colds.185 Other studies have found similar results.81,83

Many people use vitamin C for colds in a different way: they only begin taking it when cold symptoms start. Vitamin C is probably not effective when used in this way.83,140,185 One double-blind trial enrolled 400 individuals with new-onset cold symptoms, and divided them into four different daily vitamin C dosage groups: 30 mg daily (a dose lower than the minimum daily requirement, and used by the researchers as a placebo), 1,000 mg, 3,000 mg, or 3,000 mg with bioflavonoids.140 Participants were instructed to take the vitamin at the onset of symptoms and for the following 2 days. The results showed no difference in the duration or severity of cold symptoms among the groups. High-dose vitamin C taken at the onset of a cold, in other words, didn't help. A review of 7 randomized and non-randomized trials also found that taking vitamin C at the start of a cold did not offer any benefits.185
The bottom line: If you want to use vitamin C to take the edge off your colds, take the supplement throughout the winter.

There are numerous other natural treatments for the common cold as well, some of which may be more helpful than vitamin C. For more information, see the full
Colds and Flus
article.

Preventing Colds

Although two relatively recent studies suggest that regular use of vitamin C throughout the cold season can help prevent colds,167-168 they suffer from a variety of flaws, and most other studies have found little to no benefit along these lines.146

However, people who are truly vitamin C-deficient, such as elderly people in nursing homes, may show increased resistance to infection if they take vitamin C (or other nutrients).86

In addition, vitamin C might be helpful for preventing the respiratory infections that can follow heavy endurance exercise. Marathon running and similar forms of exertion can temporarily weaken the immune system, leading to infections. Vitamin C may be helpful. According to a double-blind, placebo-controlled study involving 92 runners, taking 600 mg of vitamin C for 21 days prior to a race, made a significant difference in the incidence of sickness afterwards.87
Within 2 weeks of the race, 68% of the runners taking placebo developed cold symptoms versus only 33% of those taking the vitamin C supplement. As part of the same study, non-runners of similar age and gender to those running were also given vitamin C or placebo. Interestingly, the supplement had no apparent effect on the incidence of upper respiratory infections in this group. Vitamin C seemed to be effective in this capacity only for those who exercised intensively!

Two other studies found that vitamin C could reduce the number of colds experienced by groups of people involved in rigorous exercise in extremely cold environments.88
One study involved 139 children attending a skiing camp in the Swiss Alps, while the other enrolled 56 military men engaged in a training exercise in northern Canada during the winter months. In both cases, the participants took either 1 g of vitamin C or placebo daily at the time their training program began. Cold symptoms were monitored for 1 to 2 weeks following training, and significant differences in favor of vitamin C were found.

However, one very large study of 674 US Marine recruits in basic training found no such benefit.89
The results showed no difference in the number of colds between the treatment and placebo groups.

What's the explanation for this discrepancy? There are many possibilities. Perhaps basic training in the Marines is significantly different from the other forms of exercise studied. Another point to consider is that the Marines didn't start taking vitamin C right at the beginning of training, but waited 3 weeks. The study also lasted a bit longer than the positive studies mentioned above, continuing for 2 months; maybe vitamin C is more effective at preventing colds in the short term. Of course, another possibility is that it doesn't really work. More research is needed to know for sure.

Preeclampsia Prevention

Preeclampsia is a dangerous complication of pregnancy that involves high blood pressure, swelling of the whole body, and improper kidney function. A double-blind, placebo-controlled study of 283 women at increased risk for preeclampsia found that supplementation with vitamin C (1,000 mg daily) and vitamin E (400 IU daily) significantly reduced the chances of developing this disease.96

While this research is promising, larger studies are necessary to confirm whether vitamins C and E will actually work. The authors of this study point out that similarly sized studies found benefits with other treatments, such as aspirin, that later proved to be ineffective when large-scale studies were performed. Furthermore, keep in mind that we don't know whether such high dosages of these vitamins are absolutely safe for pregnant women.

Cancer Treatment

Cancer treatment is one of the more controversial proposed uses of vitamin C. An early study tested vitamin C in 1,100 terminally ill cancer patients. One hundred patients received 10,000 mg daily of vitamin C, while 1,000 other patients (the control group) received no treatment. Those taking the vitamin survived more than four times longer on average (210 days) than those in the control group (50 days).102 A large (1,826 subjects) follow-up study by the same researchers found a nearly doubled survival rate (343 days versus 180 days) in vitamin C-treated patients whose cancers were deemed "incurable," as compared to untreated controls.103 However, these studies were poorly designed, and other generally better-constructed studies have found no benefit of vitamin C in cancer.104,105
At the present time, vitamin C cannot be regarded as a proven treatment for cancer.

Reflex Sympathetic Dystrophy

Reflex sympathetic dystrophy (RSD) is a set of symptoms that can develop in the legs, arms, feet, and hands after fractures and other injuries. Also called complex regional pain syndrome (CRPS), symptoms include changes in skin temperature and color over the affected area, accompanied by burning pain, sensitivity to touch, sweating, and limitation of range of motion. The cause of RSD is unknown, and the condition is very difficult to treat.

Two studies performed by a single research group reported evidence that vitamin C can help prevent RSD after wrist fractures.110,180

In one of these, a total of 123 adults with wrist fractures were enrolled and followed for one year.110
All were given 500 mg of vitamin C or placebo daily for 50 days. The results showed significantly fewer cases of RSD in the treated group.

A subsequent study conducted by the same research group compared placebo against three dosages of vitamin C in 416 people suffering from wrist fracture.180
Again, treatment continued for 50 days. The results indicated that approximately 10% of those given placebo developed RSD, while less than 2% of those given either 500 mg or 1,500 mg of vitamin C daily did so. According to the statistical analysis used by the authors, this relative benefit was statistically significant. The 200 mg dose of vitamin C did appear to offer some protection too, but not as much.

Easy Bruising

A 2-month, double-blind study of 94 elderly people with marginal vitamin C deficiency found that vitamin C supplements decreased their tendency to
bruise.111

Hypertension (High Blood Pressure)

According to a 30-day, double-blind study of 39 individuals taking medications for
hypertension, treatment with 500 mg of vitamin C daily can reduce blood pressure by about 10%.112 Smaller benefits were seen in studies of individuals with normal blood pressure or borderline hypertension.113,114,148 However, other studies have failed to find any significant blood pressure-lowering effect.115,116,147
This mixed evidence suggests, on balance, that if vitamin C does have any blood pressure-lowering effect, it is at most quite small.

Maintaining the Effectiveness of Nitrate Drugs

Nitroglycerin and related nitrate medications are used for the treatment of angina. However, the effectiveness of these medications tends to diminish over time. According to a double-blind study of 48 individuals, use of vitamin C at a dose of 2,000 mg 3 times daily helped maintain the effectiveness of nitroglycerin.142 These findings are supported by other studies as well.143-145

Note: Angina is too serious a disease for self-treatment. If you have angina, do not take vitamin C (or any other supplement) except on a physician’s advice.

Safety Issues

The US government has issued recommendations regarding tolerable upper intake levels (ULs) for vitamin C. The UL can be thought of as the highest daily intake over a prolonged time known to pose no risks to most members of a healthy population. The ULs for vitamin C are as follows:

Children

1-3 years: 400 mg

4-8 years: 650 mg

9-13 years: 1,200 mg

Males and Females

14-18 years: 1,800 mg

19 years and older: 2,000 mg

Pregnant Women

18 years old or younger: 1,800 mg

19 years and older: 2,000 mg

Nursing Women

18 years old or younger: 1,800 mg

19 years and older: 2,000 mg

However, even within the safe intake range for vitamin C, some individuals may develop diarrhea. This side effect will likely go away with continued use of vitamin C, but you might have to cut down your dosage for a while and then gradually build up again.

Concerns have been raised that long-term vitamin C treatment can cause
kidney stones.129,130,163 However, in large-scale observational studies, individuals who consume large amounts of vitamin C have shown either no change or a decreased risk of kidney stone formation.131-133 Still, there may be certain individuals who are particularly at risk for vitamin C-induced kidney stones.134
People with a history of kidney stones and those with kidney failure who have a defect in vitamin C or oxalate metabolism should probably restrict vitamin C intake to approximately 100 mg daily. You should also avoid high-dose vitamin C if you have glucose-6-phosphate dehydrogenase deficiency, iron overload, or a history of intestinal surgery.

Vitamin C supplements increase absorption of
iron.121-128,164
Since it isn’t good to get more iron than you need, individuals using iron supplements shouldn’t take vitamin C at the same time except under a physician’s supervision.

One study from the 1970s suggests that very high doses of vitamin C (3 g daily) might increase the levels of
acetaminophen (such as Tylenol) in the body.135
This could potentially put you at higher risk for acetaminophen toxicity. This interaction is probably relatively unimportant when acetaminophen is taken in single doses for pain and fever, or for a few days during a cold. However, if you use acetaminophen daily or have kidney or liver problems, simultaneous use of high-dose vitamin C is probably not advisable.

Weak evidence suggests that vitamin C, when taken in high doses, might reduce the blood-thinning effects of
warfarin
(Coumadin)
and
heparin.136-139

As noted above, one study found that vitamin C at a dose of 1 g daily substantially reduced blood levels of the drug indinavir, a protease inhibitor used for the treatment of HIV infection.165

Heated disagreement exists regarding whether it is safe or appropriate to combine antioxidants such as vitamin C with standard chemotherapy drugs. The reasoning behind the concern is that some chemotherapy drugs may work in part by creating free radicals that destroy cancer cells, and antioxidants might interfere with this beneficial effect.76,166 However, there is no good evidence that antioxidants actually interfere with chemotherapy drugs, but there is growing evidence that they do not.77,79,151

The maximum safe dosages of vitamin C for people with severe liver or kidney disease have not been determined.

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.